The offspring of monkey mothers are being obtained on weaning at 4 mo. of age from other research projects in which the mothers have been exposed to various types and doses of PCBs (Aroclor 1248, Aroclor 1016, or PCB residues from fish meal diets). These offspring will be reared normally, along with control offspring unexposed to PCBs, and will be tested (as they age and develop) on a series of behavioral tests chosen to detect whether any neurological or other possible toxic effects of the PCBs may have altered the behavioral competence or characteristics of the monkeys. Behavioral tests which are planned include activity measures of motivation, learning behavior, and social behavior. The monkey is most pertinent with respect to estimating the toxicity of PCBs, since it seems to be like the human in the way it metabolizes these compounds, and since it appears to be as sensitive to the toxicity of these compounds as is the human. The behavioral complexity of the monkey also approaches that of the human. It is planned to obtain estimates of threshold levels of PCBs which produce neurobehavioral toxicity,and also to determine whether permanent deficits are produced by PCB exposure early in the life of the primate.